The disclosure is explained below with reference to an internal gear pump, but in principle it can be applied also to gear pumps in general, i.e. also to external gear pumps. Internal gear pumps have an externally toothed gearwheel which, for unambiguous designation, is referred to below as the pinion, and an internally geared so-called crown wheel, wherein the pinion is arranged eccentrically in the crown wheel so that the two gearwheels, i.e. the pinion and the crown wheel, can intermesh together in a peripheral portion. On another peripheral portion there is a sickle-shaped clearance between the two gearwheels, which is delimited on the inside by the pinion and on the outside by the crown wheel. The clearance is also called the pump chamber or compression chamber. Due to the rotational drive of the two gearwheels, wherein usually the pinion is held rotationally fixed on a pump shaft which is driven in rotation, and via the pinion the crown wheel is also driven rotationally, fluid is conveyed from a suction region to a pressure region of the pump chamber located behind this in the direction of rotation of the gearwheels. A pump inlet opens in the suction region and a pump outlet branches from the pressure region.
At the side i.e. on the faces of the gearwheels, side walls delimit the pump chamber. The side walls can also be called the end walls, covers or similar. An example of such an internal gear pump is disclosed in patent DE 196 13 833 B4. To seal the pump chamber at the faces of the gearwheels, the known internal gear pump has discs known as axial discs which are rotationally fixed and lie against the gearwheels with their insides facing the gearwheels. On the outsides of the axial discs, pressure fields are provided which are pressurized with fluid from the pressure region of the internal gear pump. The pressure fields are flat depressions which extend in a sickle shape over approximately the pump chamber or part of the pump chamber. The pressure fields can be formed in the outsides of the axial discs and/or in the insides facing these of the side walls of the internal gear pump. The axial discs are held rotationally fixed. The pressure of the fluid conveyed presses the axial discs against the faces of the gearwheels of the internal gear pump in order to seal the pump chamber. This does not achieve a hermetic seal but a good compromise between low leakage, good lubrication and low friction between the rotating gearwheels and the fixed axial disc, and low wear.
Lubrication between the faces of the gearwheels of the internal gear pump and the axial discs lying thereon and pressurized from the outside is provided in the manner of hydrodynamic lubrication by fluid which adheres to the faces of the gearwheels and is conveyed by the gearwheels between the axial discs and the faces of the gearwheels.